Most gaming at the moment tends to use 1 primary core and offload some minor processes to secondary cores. The long and short of it is that the game will only really be impacted by the maximum single core speed. Having more cores doesn't really make any odds.
There are a few games now that are more core reliant, and can make decent use out of multiple cores. Turn based games are pretty good at using the cores heavily, but not in a justifiable way for the price difference.
In the future, games will hopefully make better use of the multi-cores. We believe this is highly likely as it seems supported by the consumer chip core-count across the board (at enthusiast level).
With allllll of that in mind, the 12600K is still a fantastic choice as it's still a 10 core chip. No matter which way you slice it, it's going to be an excellent performer for a number of years. The core speed of 4.9Ghz has it performing very well for all gaming scenarios including Flight Sims.
With your use case, anything above is a bit of a waste of cash really as there's nothing you're going to do that's going to warrant a higher end chip.
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